IMPROVED LIQUID PHASE SEPARATOR WITH CLEAN-UP COLUMN
Abstract
A simple modification of liquid phase separator with integrated clean-up column for water analysis
is presented. The modification enables treatment of strong emulsions and speeds up the sample
preparation. The use of separator is demonstrated in the analysis of polycyclic aromatic hydrocarbons
in water sample.
Key words: liquid phase separator; water analysis; sample preparation
1. Introduction
Among the variety of techniques intended for preconcentration and isolation of organic
substances from water matrix, liquid-liquid extraction (LLE) is still in frequent use. LLE
comprises a mixing and a separation step. After the mixing step the two immiscible liquids
with different specific gravities are commonly separated using appropriate separator [1-3].
Due to the fact that the resulting solvent extract phase contains some amount of water
and in the case of treatment of dirty samples it also contains undesirable interfering substances;
it is necessary to include a drying and clean-up step before the chromatographic analysis.
Recently, for the separation and treatment of solvent extract layer after the extraction
of organic compounds from water, the liquid phase separator with chromatographic column
has been developed [4]. This separator speeds up and simplifies the sample preparation
procedure because both the separation and treatment steps are accomplished in one
simple run in a single peace of glassware. The disadvantage of this separator arises in
the case of formation of strong emulsions. To perform well also in treating strong emulsions,
the separator was simply modified.
2. Results and discussion
In Figs. 1 and 2 the improved liquid phase separator with integrated clean-up column
is illustrated. The separator consists of a top neck with a sintered glass bottom (operates
as a clean-up column), filling tube for water and male joint. After the completion of extraction,
the separator is connected to the extraction flask and through the filling tube attached
via flexible tubing to a water reservoir, pure water is added. The added water causes the
solvent layer to rise through the packing of the clean-up column and the treated extract
from the top of the column can be concentrated and analyzed directly.
The main difference between the previous design and the new one is that the side arm
for water from the former is replaced by flexible tubing connected to the larger water
reservoir in the latter. This modification results in substantial increase of hydrostatic
pressure. Greater water pressure makes the solvent extract layer easier to overcome the
resistance to flow in the clean-up column. This speeds up the treatment and separation procedure
and is of great importance when strong emulsions are treated and large amounts
(up to 30 g) of anhydrous sodium sulphate are used. In the case of normal and emulsion
forming samples, separators with smaller (e.g. 10 cm long, 1.7 cm I.D.) and larger (e.g.
10 cm long, 2.7 cm I.D.) internal diameter clean-up columns can be used (for application
of different amounts of treatment material).
Figure 1. Liquid phase separator with
clean-up column: (1) clean-up column, (2)
sintered glass frit, (3) filling tube for water,
(4) male joint.
Figure 2. Separator in operation: (1) liquid
phase separator, (2) separated extract, (3)
anhydrous sodium sulphate, (4) sintered
glass frit, (5) extraction flask, (6) flexible
tubing, (7) water reservoir.
The modified separator is a very helpful tool in trace analysis of organic contaminants
in water samples when LLE is performed with solvents lighter than water. The separation
and treatment of the solvent extract is fast and can be completed within a few minutes.
The simple design of the separator makes its cleaning easier, which also speeds up the work.
In our laboratory, the liquid phase separator is used in sample treatment for the determination
of polycyclic aromatic hydrocarbons (PAHs), phthalates, alkyl phenols, polychlorinated
biphenyls, organochlorinated pesticides or hydrocarbon oil index. Fig. 3 shows an example of
chromatograms from the determination of PAHs (A) and phthalates (B) in surface water
sample. 1 L of water sample was transferred into a 1-L Erlenmeyer flask and 5 g of sodium
chloride and 5 mL of 50% (v/v) sulphuric acid aqueous solution were added.
Figure 3. Chromatograms from the HPLC determination of PAHs and phthalates in surface water
sample using (A) fluorescence and (B) UV detection. Peaks: (1) phenanthrene, (2) anthracene,
(3) fluoranthene, (4) pyrene, (5) benzo[a]anthracene, (6) chrysene, (7) benzo[b]fluoranthene,
8) benzo[k]fluoranthene, (9) benzo[a]pyrene, (10) dibenzo[a,h]anthracene, (11) benzo[g,h,i]perylene,
(12) indeno[1,2,3-cd]pyrene, (13) bis(2-ethylhexyl) phthalate.
Peter Tölgyessy et al./Petroleum & Coal 51(4), 282-285, 2009 283
Then, after addition of a stirring bar and 10 mL of hexane, the flask was closed with a
ground stopper and thoroughly mixed using a magnetic stirrer at maximum setting for 2
hours. The solvent layer was separated and dried using the liquid phase separator with
clean-up column filled with 10 g of anhydrous sodium sulphate. Then the treated extract
was evaporated to dryness, redissolved in 200 μl of acetonitrile and 15 μl aliquot of the
final extract was analysed by HPLC using both fluorescence (for PAHs) and UV (for phthalates)
detection.
References
[1] Hrivňák, J.: Solvent thin layer separator for microextraction of water. Anal. Chem.
57 (1985) 2159-2160.
[2] ISO 9377-2 Water quality. Determination of hydrocarbon oil index. Part 2. Method
using solvent extraction and gas chromatography. International Organization for
Standardization, Geneva, Switzerland, 2000.
[3] Kotianová, P., Matisová, E.: Liquid-phase microextraction and its utilization for
trace analysis of organic compounds in water matrix. Chem. Listy (Chemical Papers)
94 (2000) 220-225.
[4] Mikita, M., Tölgyessy, P., Hrivňák, P.: Liquid phase separator with chromatographic
column. J. Chromatogr. A 1059 (2004) 223-224.